For a hybrid vehicle utilizing an internal combustion engine, a dual-clutch transmission, and an electric machine delivering torque to driven wheels after the transmission, there can be powertrain modes that propel the vehicle using only the electric machine with the transmission input clutches open, allowing the engine to be stationary and off. If the vehicle is being driven in such a mode at non-zero speeds, and the total powertrain output torque request exceeds the propulsion capability of the electric machine, the engine may be started to deliver additional torque to the driveline.
It can be challenging to add the engine torque to the driven wheels smoothly and as quickly as possible to reduce delays between a driver's input and/or expectations, and the actual vehicle acceleration response. In some cases, the engine may be connected to driven wheels through a higher transmission gear ratio to achieve higher torque multiplication required to meet high total powertrain output torque requests. At higher vehicle speeds, the higher gear ratio may result in a higher input shaft rotational speed that the engine may have to match to lock the input clutch and transmit the requested torque to the driven wheels. However, because the engine is starting from zero speed, it may take some time to start combustion and accelerate its inertia up to the required speed to lock the input clutch. While the engine is accelerating up to the target speed, it may not be transmitting any torque to the driven wheels, which may result in a delay between the request for engine torque, and the engine transmitting torque to the wheels.
The inventors herein have recognized these issues, and have developed systems and methods to at least partially address the above issues. In one example, a driveline operating method is provided, comprising controlling a first target input shaft of a dual clutch transmission to a first speed, while controlling a second non-target input shaft of the dual clutch transmission to a second speed, wherein the first speed is greater than the second speed, and transmitting torque to driven vehicle wheels via an engine configured to propel the vehicle by connecting an engine crankshaft to the second non-target input shaft while the engine is increasing speed to the first speed. In this way, a delay between a request for engine torque, and the engine transmitting torque to the wheels, may be reduced.
As an example, controlling the first target input shaft to the first speed includes engaging a first target gear with the first target input shaft, and wherein controlling the second non-target input shaft to the second speed includes engaging a second non-target gear with the second non-target input shaft. In such an example, engaging the first target gear with the first target input shaft and engaging the second non-target gear with the second non-target input shaft occur either while the engine is off and the vehicle is being propelled solely via the electric machine, or subsequent to the engine startup event to deliver additional torque to the driveline.
As one example, the driveline operating method may comprise propelling the vehicle solely via an electric machine positioned downstream of the dual clutch transmission while the engine is off, under conditions where a wheel torque demand can be met solely via the electric machine. In such an example, transmitting torque to the one or more driven wheels by connecting the engine crankshaft to the second non-target input shaft while the engine is increasing speed may occur responsive to a driveline torque request exceeding the capability of the electric machine that results in an engine startup event to deliver additional torque to the driveline.
In one example, responsive to the driveline torque request exceeding the capability of the electric machine, the method may further comprise increasing torque provided to the driven wheels via the electric machine to an electric machine maximum torque limit (e.g. maximum torque threshold), the maximum torque limit/threshold determined based on one or more of at least a state of charge of an onboard energy storage device, and a temperature of the electric machine.
As another example, the method may further comprise fully disconnecting the engine crankshaft from the second non-target input shaft, and connecting the engine crankshaft to the first target input shaft responsive to engine speed being synchronized with the first speed. In such an example, the engine crankshaft may be connected to the first target input shaft via a first target clutch, and wherein connecting and fully disconnecting the engine crankshaft from the second non-target input shaft is via a second non-target clutch.
In this way, while the engine is accelerating up to the first speed, or target speed, torque may be transmitted to the driven wheels, thus reducing the delay between the request for engine torque, and the engine transmitting torque to the wheels.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.